Beta-alanine is a nonessential amino acid thought to be a precursor to carnosine in muscle tissue. Carnosine
buffers hydrogen ions, making muscle tissue less acidic and delaying fatigue. Thus it is thought
delay the onset of the "burn" one experiences with extreme exercise. Although blamed on lactic acid
accumulation, it is probably other acid byproducts of metabolism that are the real culprit behind this discomfort.

Interestingly women have much less carnosine in their muscles than men, thus one idea is that supplementation with beta-alanine might be more beneficial in this group of athletes. Does it work?

A recent study suggests that it does. "In their study, Glenn and his colleagues randomly assigned 11 female masters cyclists to beta-alanine 800 mg and 11 to placebo four times a day for 28 days....The researchers assessed peak oxygen consumption as each cyclist rode a cycle ergometer....At baseline and during the first three weeks of the study, these measurements were not significantly different between the two groups. However, by the end of the fourth week, changes in endurance became significantly greater in the beta-alanine than in the placebo group, although hand-grip strength did not change significantly in either group."

And this finding (of increased work output on beta alanine) was supported by a meta analysisof 19 randomized studies. The findings "...appear to support that BA may increase power output and working capacity, decrease the feeling of fatigue and exhaustion, and have of positive effect on body composition and carnosine content."

Side effects? A quick review of the online literature (much of it anecdotal) mentions only paresthesias (numbness and tingling). These were documented in one published medical study. And in another the daily beta-alanine was divided into 4 doses to avoid this side effect.

As you read this article, remember the various caveats:

work has shown that acute supplementation does NOT improve anaerobic performance.

these were a very clearly defined group of highly trained athletes. Would recreational riders notice a difference? Yes. A specific study looking at short term anaerobic output (where a hydrogen buffering effect would be more noticeable) indicated that both trained and non trained individuals would benefit.

these were women, with a lower baseline level of carnosine at the start. Would men notice a difference, and at 4 weeks?

carnosine levels decrease with age suggesting that just as with creatine, older athletes might benefit to a greater degree.

The finding will almost certainly lead to further investigations. For now, it's unclear how these findings translate into real life training programs.